1. Field of the Invention
The present invention relates to a combustor of a gas turbine, specifically to a combustor in which a peripheral wall is cooled by steam.
2. Description of the Prior Art
FIG. 3 is a constructional view of a conventional gas turbine plant. In FIG. 3, numeral 6 designates a compressor, numeral 7 designates a combustor, numeral 8 designates a gas turbine connected to the compressor 6 coaxially and numeral 9 designates an exhaust gas boiler for recovering energy of the exhaust gas after being used for driving the gas turbine 8.
In operation of the gas turbine plant constructed as mentioned above, combustion air which has been compressed by the compressor 6, driven coaxially with the gas turbine 8, is led into the combustor 7. In the combustor 7, fuel is injected for combustion into the compressed combustion air. Combustion gas therefrom is led into the gas turbine 8 for expansion and then is led into the exhaust gas boiler 9. It is to be noted that, although not shown in the figure, a generator is connected to an output shaft of the gas turbine 8 to be driven by the gas turbine 8 so as.
In the exhaust gas boiler 9, water is heated by the exhaust gas sent from the gas turbine 8 to generate steam. This steam is led into and drives a steam turbine (not shown). Also, a portion of the steam is led into the combustor 7 as cooling steam to be used for cooling of a peripheral wall of the combustor 7.
FIG. 4 is a cross sectional view of a main part of one example of a prior art combustor, in which a peripheral wall of the combustor is cooled by cooling steam. In FIG. 4, the combustor 7 of the steam-cooled system is a combustor for generating a combustion gas of a high temperature, about 1,500.degree. C., at the gas turbine inlet. Numeral 2 designates a peripheral wall, which is a steam-cooled wall constructed such that steam flows in the wall for cooling of the wall surface. The steam has been generated at the exhaust gas boiler 9 to do expansion work in a steam turbine (not shown) and thus has been temperature-reduced to a certain level to be used as the cooling steam.
Numeral 10 designates a combustion chamber, which is surrounded by the peripheral wall 2 and constructed such that combustion air from the compressor 6 is led thereinto through a wall portion 20 on an upstream side thereof. Also, in the wall portion 20 on the upstream side of the combustion chamber 10; there is provided a pilot nozzle 4 at a central portion thereof. Also provided are a plurality of main nozzles 3, arranged with equal intervals along a circumferential direction of the combustor 7; on an outer side of the pilot nozzle 4. Numeral 2a designates a combustion gas outlet.
In operation of the combustor 7 constructed as mentioned above, fuel is injected from the pilot nozzle 4 into the combustion air in the combustion chamber 10 to be ignited and then main fuel is injected from the plurality of main nozzles 3 into the flame so ignited to be mixed and burned with the air in the combustion chamber 10 and generate combustion flame 5. Combustion gas so generated flows out of the outlet 2a of the combustion chamber 10 to be sent to the gas turbine 8 for drive thereof.
There are, however, shortcomings as mentioned below in the prior art gas turbine combustor of a steam-cooled system shown in FIG. 4. That is, there is formed a low velocity zone of fuel and air flow in the vicinity of the inner surface of the peripheral wall 2 on an upstream side in the combustion chamber 10. The fuel concentration in this low velocity zone, which is shown as "B" in FIG. 4, is liable to become higher (thicker). Hence, the flame 5 generated at the low velocity zone B spreads toward the upstream side, that is, toward the nozzles 3, 4, along the vicinity of the inner surface of the peripheral wall 2, so that a combustion is caused there in which the mixing of fuel and air is incomplete, or a combustion is caused there in which a cross sectional combustion load is high. As a result, in the gas turbine using the prior art combustor 7, there arise problems of an increased discharge of NO.sub.x (nitrogen oxides) due to an elevation of combustion temperature, an increase of combustion vibration due to rapid combustion, etc. in the combustion chamber 10.